Contact and arc runner structure for circuit interrupting devices



Feb. 9, 1954 Filed Dec. 50 195 raf/7 A. C. CONTACT AND ARC RUNNERSTRUCTURE KELLE FOR CIRCUIT INTERRUPTING DEVICES 2 Sheets-Sheet l Feb.9, 1954 A c. KELLE 2,668,892

CONTACT AND'ARC RUNNER STRUCTURE FOR CIRCUIT INTERRUPTING DEVICES FiledDec. 50, 195C `2 Sheets-Sheet 2 Patented Feb. 9, 1,954

CONTACT AND ARC RUNNER STRUCTUREy FOR CIRCUIT INTERRUPTING DEVICESArthur C. Kelle, Stoughton, Mass., assignor to Allis-ChalmersManufacturing Company, Milwaukee, Wis.

ApplicationDecember 30, 1950, Serial No. 203,613

6 Claims. (Cl. 20G- 147) This invention relates to circuit interruptingdevices and more particularly to an arc chute and contact structure usedin connection therewith.

In the construction and operation of air magnetic breakers, it isimportant to design the breaker so that it transfers in a minimum lengthor time the arc from the point of its inception within the arc chute tothe point where nal arc extinction is to take place. Equally importantis the necessity of designing the circuit interrupter so as to achieve achute structure which comes relatively close to the desideratum of eventhermal duty distribution.

Therefore, in accordance with the invention claimed a new and improvedcircuit interrupter is provided comprising an arc chute and a pair ofcooperating contacts between which a gap is formed and an arc is ignitedwhen the circuit is interrupted. The contacts comprise a slotted hornshaped fixed arcing contact and a horn shaped movable arcing contactrmly engaging the slot walls of the xed arcing contact when in thecircuit closed position. The fixed arcing contact is flexibly mounted soas to align itself when engaging the movable arcing contact. A flatmetallic head runner is mounted adjacent the xed arcing contact fortransferring the arc from the xed arcing contact to a region remotetherefrom and a tail runner is arranged to transfer the arc from themovable arcing contact to a region remote therefrom. A blowout meanssuch as a magnetic coil is used to transfer the arc terminal from themovable arcing contact to the tail runner when the gap between thearcing contacts and in turn the arc is of a predetermined length.

The are is initially rapidly elongated in a direction perpendicular tothe longitudinal axis of the barrier plates with a minimum of arcpropulsion in a direction toward the exhaust end of the lare chutestructure. This initial rapid substantially straight are elongation isachieved within an expansion space which is situated below thetransverse barrier plates of the chute'. Hence preheatng of the barrierplates is eiectively avoided during the above initial period of arcelongation.

It is, therefore, one object of the present invention to provide a newand improved arc interrupting"device in which the arcing contacts areself-aligning.

'Another object of this invention is to provide a new "and improved arcinterrupting device .in Whichth'e.relatvelyxed arcing cQntactand arerunner structure is broken up into two nonintegrated or substantiallyseparate parts.

A further object of this invention is to provide a new and improved arcinterrupting device in which the movable horn shaped arcing contact isso designed and positioned in the device that it equally distributes thecooling duty of the arc chute throughout its structure.

A still further object of this invention is to provide a new andimproved arc interrupting device in which the arc is initially rapidlyelongated in a direction perpendicular to the axis of the barrier platesof the arc chute with a minimum of arc propulsion in a direction towardthe exhaust end of the arc chute structure.

A still further object of this invention is to move the arc into the arcchute in such a manner that each barrier plate equally distributes theheat of the arc.

A still further object of this invention is to eliminate arcing betweenthe tertiary and arcing contacts.

Objects and advantages other than those above set forth Will be apparentfrom the following description when read in connection with theaccompanying drawing, in which:

Fig. l is a view in cross section, of a magnetic blowout type of circuitbreaker employing the present invention;

Fig. 2 is a front View of the head runner shown in Fig. 1;

Fig. 3 is a side View of the head runner shown in Fig. 2;

Fig. 'l is a front view of the tail runner shown in Fig. 1;

Fig. 5 is a side view of the tail runner shown in Fig. 4;

Fig. 6 is an enlarged view of the arcing contact structure shown in Fig.1;

` Fig. 7 is an end view of the contact structure shown in Fig. 6 withthe movable arcing contact omitted for the sake of clearness Fig. 8 is apartial plan View of the stationary arcing contact structure shown inFigs. 1, 6 and 7 with parts thereof in cross section;

Fig. 9 is a plan View of the tertiary contact structure taken along theline IX--IX of Fig. 6;

Fig. lO-is a side View of the stationary arcing contact structure shownin Figs. 1 and 6; and

Fig. 11 is an end view of the elements shown in Fig. 10 looking from theleft.

Referring more particularly to the drawings by characters of reference,Fig. l illustrates a magnetic blowout type of circuit breaker includ-Aing as elements thereof a pair of terminal studs i6 and l? forconnecting the circuit breaker to line conductors (not shown). Althoughin general, circuit breakers of the type considered in Fig. l areprovided with a plurality of similar pole structures, one for each phaseof a polyphase electric circuit, only one such pole structure is shownin the drawing and the circuit breaker will be described in detail as ifit was of the single pole unit type,

The circuit interrupter or breaker in Fig. 1 comprises essentially meansfor opening the circuit to form the interrupting arc and an arcextinguishing structure. Speciiically, the circuit opening meanscomprises a .iixed contact assembly supported on an insulator I5 andincluding a current carrying contact I8, tertiary contacts I9, and anaroing contact 2|), cooperating with a movable contact 2| comprisingcurrent carrying, tertiary and arcing contacts combined in a singlestructure. Arcing contact 2| is mounted on a lever 22 which is pivotallymounted at 23 on an extension 24 of the circuit breaker stud I6 and isoperated by means of a reciprocally movable rod 25. The operating rod 25is suitably connected to an actuating mechanism (not shown) foroperating the movable contact between closed and open circuit positions.Fig, l. illustrates the movable contact 2| in closed position. Thearcing contacts are electrically connected to the lower ends of terminalstuds lli and l1. Accordingly, when the breaker is connected in seriesin a power circuit and the arcing contacts are separated, an arc may beinitiated across the gap formed between the contacts.

For the purpose of interrupting this power arc, an arc extinguishingstructure, such as an arc chute 30, may be mounted so as to receive thepower arc which is under the influence of a inagnetic blowout means. Thearc chute preferably is disposed about and directly above the arcingcontacts, as shown, when the blowout means act upward, but may bemounted in any other suitable location when the blowout means act inother directions. The magnetic blowout structure can assume anypreferred form so that a brief description thereof will be sufficient.The magnetic blowout means may comprise a core 3|, poles 32, and a coil33. The latter is electrically connected to the terminal stud I1 and,

through a strap 28, to a metallic arc runner 34 so that the arc current(as the arc travels along the runner) ows through the blowout coil in amanner well known in the art.

Normally the current is carried in the closed circuit position of thebreaker by contact 2! and the spring biased contact I While the movablearcing contact 2| is actuated to open circuit position. current isshunted from iixed contact IS first to iixed contact I 9 and then tofixed arcing contact 28. As the arc is drawn by the movable arcingcontact 2 the arc terminal on arcing contact 2l) is transferred to arcrunner 34 which is adiacent to and connected to contact 20 but separatedtherefrom by a gap 23. The arc terminal is driven across gap 29 to reacha rlat side of arc runner 34, When the movable arcing contact 2|approaches a predetermined position in its opening stroke, the other arcterminal transfers from the movable arcing contact 2| to an arc runner35 which directs the arc into the arc chute 3.

Arc runners 34 and 35 are each divided into two sections. Arc runner 34comprises a first section 'lli arranged within arc chute 3|]substantially parallel tothe direction of arc transfer .in azonerelativelyremote from the point of arcinitiaftlm,

4 and a second section 1| conductively connected to section 10 andarranged in angular relationship with respect to the direction of arctransfer and to the rst section 'I0 for transferring one terminal of thearc from the fixed arcing contact 28 to the rst section l'. Arc runner35 comprises a first section 12 arranged within arc chute 30 andparallel with section l0 of arc runner 34 but spaced therefrom at theopposite side of the arc chute, and a second section 73 arranged inangular relationship with respect to the first section l2 andconductively connected thereto for transferring the other terminal ofthe arc from the movable arcing contact 2| to the first section 12. Theslope of section 1| of arc runner 34 is smaller than the slope ofsection 13 of arc runner 35 when the longitudinal axis of the arc chuteis vertical, as in the embodiment illustrated in Fig. 1.

The sloping sections 'I and 'I3 of the arc runners 34 and 35 arearranged in an expansion space or -zone T4 which is situated below aplurality of transverse barrier plates 'l5 forming a part of arc chute30. Barrier plates 15 are arranged to form a parallelepipedic body inbetween the parallel sections 'I0 and 'l2 of arc runners 34 and 35 andprovide a oonstricted passage to retard and limit the expansion of thearc as it moves through arc chute 33. The points of juncture of arcrunner section 10 with section 'll and `of section 'l2 with section 13are disposed adjacent the entrance of the constricted passage dened bythe barrier plates at opposite ends of such entrance.

One end of the blowout coil 33 is connected to the arcing contact 20 andthe other end to tertiary contact I9. When the movable arcing contact 2|parts from contact I9, the vflow of current is transferred from contactI9 to contact 20 through the blowout coil 33. The movable arcing contact2| subsequently parts from contact 2) `to draw an arc. Accordingly, theblowout coil is already energized at the inception of the arcinterruption to influence the arc in a well known manner, i. e., todrive it into the.

L arc chute in an expanding loop. It will be apparent to one skilled inthe art that the blowout eldcan be utilized in the most efcientmanner bydisposing the iron poles 32 so as to cooperate with the blowout coil inthe conventional manner outside of the arc chute.

Referring now to Figs. 2 to 1l, fixed arcing contact 2i! is formed inthe shape of a slotted horn shaped .finger type contact which firmlygrips the movable blade-like arcing contact 2| when in circuit closedposition. Contact 28 comprising two elements 35 and 3l forming a slot 38therebetween for receiving contact 2| is supported by steel bars 39 andscrew threaded pins 40 protruding therefrom. Pins 40 have narrow neckportions 4| slidably arranged in slots 44 of steel bars 39.

Fig. 8 shows a partial plan View of the stationary arcing contactstructure 20 with parts in 'cross section, but it is to be understoodthat the. contact structure is symmetrical with respect to the medianplane of slot 38. Pins 40 are surrounded by helical springs 42which arein turn surrounded by cylindrical spring protective housings 43 of anysuitablev insulating material such as laminated synthetic resin orfiber. The steel bars 39 are supportedby blocks 46 to which they aresecured by screws 41. One terminal of shunts 48 is secured to blocks 46while the opposite terminal vol shunts 48 is arranged between Contactelements 36, 31, respectively, and sprinslrrote tive housings 43. Thussprings 42 establish contact pressure between shunts 48 and contactelements 36 and 31, respectively.

The rear ends of contact elements 36 and 31 of arcing contact 20 areprovided with bores 49 into which project the Shanks of screws 41.Screws 41 are surrounded by helical springs 50 biasing contact elements38 and 31 and tending to reduce the space left between them. The rearends of contact elements 3S and 31 are arranged in suitable guidinggrooves in a block 52 supported on insulator i5 through a block 55 ofinsulating material. The steel bars 33 are provided with slots 53 at oneend thereof. Pins 34 entering slots 53 and secured to block 52 preventundesired rotation'of steel bars 39 about the axes of screws 41. It isobvious from the foregoing that contact elements 3B and 31 of fixedarcing contact 20 are capable of being moved transversely and of beingtilted in various directions within the limits determined by the play ofneck portions 4| of pins 4) in bars 33, the play of the shanks of screws41 in bores 49 and the play of contact elements 36 and 31 in the grooves5I. A contact arrangement permitting such a freedom of adjustment isgenerally referred to as floating.

Arc runner 34, commonly known in the art as a head runner, comprising afiat metallic strip is provided with an extending bracket 51 secured toblock 52 by means of screws 33. Bracket 51 is slotted, and the rear endof Contact elements 36 and 31 enter into a gap 53 formed between theslotted end of bracket 51. The upper end of arc runner 34 is supportedby a bracket Si! and a pin 6| secured to the frame of the interruptingdevice at one end thereof.

Arc runner 35, commonly known in the art as a tail runner, comprising aiiat metallic strip is supported by the frame of the interrupting deviceon the other end of the arc chute 3i) by brackets 62 and pins 63. Thearc runner 35 being slotted at one end thereof to permit the passage ofthe movable horn shaped arcing contact 2| through the plane of therunner, is so arranged that it receives the arc terminal from themovable arcing contact 2l after the arcing contacts 20, 2l haveseparated a predetermined distance. The arc runners are constituted asflat strips on which the roots of the arc travel on the flat sides so asto increase the rate of dissipation of the heat of the arc in the arcrunners.

The tertiary1 contacts I9 (shown in Figs. 1, 6 and 9), which relievecontact i8 of any arcing upon transfer of the fiow of current to themagnetizing coil 33 energizing the magnetic blowout system, are arrangedbelow the horn shaped arcing contact elements 3S and 31 of arcingcontact 20. Tertiary contacts I3 are protected against the action of arcflames and hot gases formed at the point of break of arcing contacts 23,2| by insulating barriers @34 proiecting in cantilever fashion from leftto right. Bars 35 are arranged parallel to the tertiary iinger contactsi9 and form abutments for contact extension arms 63, which limit theinward movement of nger contacts I3. Leaf springs 61 arranged betweentertiary finger contacts I9 and bars 65 provide the required contactpressure between tertiary contacts le and the movable arcing contact 2i.

The stationary main or fixed current carrying Contact I3 is acted uponby helical springs 68 for providing a iirm engagement between contact i8and movable arcing contact 2i.

In air magnetic breakers it is desirable to achieve a. substantiallyequal distribution'of the cooling duty throughout the entire plate orstack structure forming arc chute 30. The stack of plates in arc chute30 is provided for absorbing heat and reducing the temperature of thearcing vzone. Generally, the cooling duty imposed upon certain parts ofthe stack structure is far in excess of the cooling duty imposed uponother parts of that structure. Different parts of the arc chute areexposed to the heat of the arc at different times during theinterruption of the arc, and the heat of the arc varies during itspassage through the arc chute.

To achieve a more equal distribution of the cooling duty throughout thestack structure, the horn shaped end of the movable arcing contactremote from the stationary arcing contact was increased in length. Thisresulted in earlier transfer of the arc from the movable arcing contact2| to the cooperating slanting part of the adjacent tail arc runner E35.

The theory underlying the determination of the specic increase in lengthof the arc transfer horn of the movable arcing contact is as follows:

At the time of contact separation, the arc length is virtually zero, i.e., the arc core is virtually a hot spot and the whole arc virtually afire ball. As both contact separation and arc elongation progress, thearc is progressively converted from a substantially spherical gasdischarge to gas discharge wherein length predominates, and width issmall in comparison to length.

Equalization of the cooling duly throughout the chute requires atransfer of the arc terminal on the movable contact to the cooperatingtail runner at the earliest possible time. Existence of a suitablemechanical force for arc transfer is a condition precedent to anytransfer of an arc. The mechanical force acting upon a conductor in amagnetic field is proportional to the length orf the conductor and thisis true, of course, with regard to metallic conductors as well asconductors formed by arcs. In the above referred to process ofconversion of an arc from a hot gas sphere into a hot gas column thereis a critical are length at which the magnetic action upon the arc isjust high enough for arc transfer. For this reason, the horn shaped endof the movable contact has been designed to come alongside itscooperating are runner at the time at which this critical arc length isjust being reached. If the horn shaped end of the movable contact wasmade longer, only disadvantages, but no benefits would ensue from suchan increase in length. On the other hand, if the horn shaped end of themovable contact was made shorter, as in the lower interrupting capacitydesigns of the prior art, arc transfer could not be effected at theearliest possible time as determined by magnetic force requirements. Anydelay in transferring the arc from the movable contact to itscooperating tail runner throws too large `a portion of the total coolingduty of the arc chute upon the part thereof immediately adjacent to thestationary arcing contact.

The critical `arc length at which arc transfer from the movable contactto the tail runner can be effected depends upon the particular designunder consideration, and more particularly upon the intensity andconfiguration of the magnetic field in the region of initial contactseparation. It was found for breakers of the 4 kv. range as illustratedin Figs. 1 to 11 that the critical arc length was reached when the gapformed between the arcingcontacts was about one and one half (1%)inches. An extrapolation of this finding to other air magnetic breakerswith blowout means at the point of arc initiation results in theconclusion that the critical gap length is in excess of one inch and notmore than two inches.

The above range of critical gap length may be compared with the gaplength of about three and three fourths (3%) inches which wasestablished in previous air magnetic breakers between the arcingcontacts prior to coincidence in space of the tail runner and of themovable arcing contact.

In the magnetic breaker illustrated, the speed of initial contactseparation of the arcing contacts is in the order of 12 ft./sec. By thetime the horn shaped extension of the movable'arcing contact coincidesin space with the tail runner, the speed of the former has increased tothe order of 22 ft./sec.

Under normal interrupting conditions an arc is initiated immediatelyupon separation of the arcing contacts 20 and 2l. The terminal of thearc on xed arcing contact 20 is driven over arc runner 34 toward theexhaust end of arc chute 35i by the magnetic blowout means and thethermal effect of the arc. When the movable arcing contact 2l hasseparated a predetermined distance from the xed arcing contact 2D theother terminal of the arc jumps from contact 2| to arc runner 35 and isalso driven by the blowout means and the thermal eiect of the arc towardthe exhaust end of arc chute 3i).

The point of arc initiation is relatively close to the longitudinal axisof the arc chute and to the plane of symmetry of the arc chute which isparallel to the barrier plates 15, and this plane of symmetry intersectsthe arc close to the center thereof when the aro has reached itscritical length. The arc is initially rapidly elongated in a directionperpendicular to the longitudinal axis of the barrier plates 15 with aminimum of arc propulsion in a direction toward the exhaust end of thechute structure 30. This initial rapid substantially straight arcelongation is achieved within the expansion space 'i4 which is situatedbelow the transverse barrier plates l of chute 3B. Hence, preheating ofthe barrier plates is eiiectively avoided during the above initialperiod of arc elongation.

The arc terminals are caused to reach substantially simultaneously thepoints on the arc runners 34 and Se where their direction of travelchanges from divergent to parallel. At this time the arc path issubstantially a straight line perpendicular to the planes of the barrierplates 15. The initial elongation of the are in such a way that the arcterminals reach substantially simultaneously the points where thedirections of their respective arc runners change is achieved by propercoordination of all the factors which determine the speed of travel ofthe arc terminals. These factors include the intensity of the magneticblowout field and the speed of separation of the contacts, the length ofthe movable arc horn and the length and slope of the arc runners.

There is a tendency that the time required for moving the arc terminalformed on the stationary arcing contact 20 along the inclined section Ilof the arc runner 3d be shorter than the time required for moving theother arc terminal along H the section 'i3 of the arc runner 35. Thistenden- After both arc terminals reach the ends of the inclined sectionsof thearc runners, the arc vis moved without further elongation at rightangles to the magnetic eld, i. e., in a direction parallel to the planeof symmetry of the arc chute. This motion comes close to a translatorymotion and results in a substantially equal distribution of the thermalduty among all the barrier plates, as evidenced by a fairly equaldeterioration of the plates along the entire barrier stack.

It is within the scope of this invention to introduce the terminal endsections of the arc into the barrier plates either simultaneously withor after the introduction of the center section of the arc into thebarrier plates, but before the center section of the arc has materiallyheated the barrier plates.

Although but one embodiment of the present invention has beenillustrated and described, it will be apparent to those skilled in theart that various changes and modifications may be made therein withoutdeparting from the spirit of the invention or from the scope of theappended claims.

It is claimed and desired to secure by Letters Patent: i

l. An electric circuit interrupting device comprising a stationaryContact, a movable switch blade, means 'for moving said blade into andout of engagement with said stationary contact, an arc extinguishingdevice comprising a pair 0I spaced flat metallic arc runners, a pair ofcooperating arcing contacts between which an arc is ignited when thecircuit is interrupted mounted adjacent said arc extinguishing device,said arcing contacts comprising a slotted horn shaped xed arcing contactelectrically connected to said stationary contact and a relativelymovable arcing contact comprising a portion of said blade Contact firmlyengaging the slot walls of said fixed arcing Contact when in circuitclosed position, means for flexibly mounting said xed arcing contact forself-alignment during contact engagement with said movable arcingcontact, said biade actuating means separating said arcing contactsimmediately following disengagement of said blade from said stationarycontact during circuit opening operation, and insulating shield meansarranged between said stationary contact and said horn shaped fixedarcing contact to protect said stationary contact from arc names and hotgases formed at the point of break of said arcing contacts.

2. An electric circuit interrupting device comprising a stationarycontact, a movable switch blade, means for moving said switch blade intoand out of engagement with said stationary contact, an arc extinguishingdevice comprising a pair of spaced flat metallic arc runners,cooperating iixed and movable arcing contacts between which an arc isignited when the circuit is interrupted mounted adjacent said arcextinguishing device, said arcing contacts comprising a slotted hornshaped xed arcing contact electrically connected to said stationarycontact and a movable arcing contact comprising a portion of said switchblade iirmly engaging the slot walls of said fixed arcing contact whenin circuit closed position, means for iexibly mounting said xed arcingcontact for self-alignment during contact engagement with said movablearcing Contact, said switch blade actuating means separating said arcingcontacts immediately following disengagement of said switch blade fromsaid stationary contact during circuit opening operation, insulatingshield means arranged between said stationary contact and said horn 9shaped fixed arcing contact to protect said stationary contact from arcflames and hot gases formed at the point ofr break of said arcingcontacts, said arc runners transferring said arc from the region of arcinitiation to a region remote therefrom, one of said runners arrangedadjacent to but spaced from said fixed arcing contact.

3. An electric circuit interrupting device coniprising a stationarycontact, a movable switch blade, means for moving said switch blade intoand out of engagement with said stationary contact. an arc extinguishingIdevice comprising a pair of spaced fiat metallic arc runners,cooperating fixed and movable arcing contacts between which an arc isignited when the circuit is interrupted mounted adjacent said arcextinguishing device, said arcing contacts comprising a slotted hornshaped fixed arcing contact electrically connected to said stationarycontact and a movable arcing contact comprising a portion of said switchblade firmly engaging the slot walls of said fixed arcing contact whenin circuit closed position, means for iiexibiy mounting said fixedarcing contact for self-alignment during contact engagement with saidmovable arcing contact, said switch blade actuating means separatingsaid arcing contacts immediately following disengagement of said switchblade from said stationary contact during circuit opening operation,insulating shield means arranged between said stationary contact andsaid horn shaped xed arcing contact to protect said stationary contactfrom arc flames and hot gases formed at the point of break of saidarcing contacts, said arc runners comprising a head runner fortransferring the arc from said fixed arcing contact to a region remotetherefrom and a tail runner for transferring the arc from said movablearcing contact to said region remote therefrom, and blowout means fortransferring the arc from said movable arcing contact to said tailrunner.

4. An electric circuit interrupting device comprising a stationarycontact, a movable switch blade, means for moving said switch blade intoand out of engagement with said stationary contact, an arc extinguishingdevice comprising an arc chute, a plurality of barrier plates arrangedwithin said arc chute, and a pair of spaced fiat metallic arc runners,cooperating lixed and movable arcing contacts between which an arc isignited when the circuit is interrupted mounted adjacent said arcextinguishing device, said arcing contacts comprising a slotted hornshaped iixed arcing contact electrically connected to said stationarycontact and a movable arcing contact comprising a portion of said switchblade rmly engaging the slot walls of said fixed arcing contact when incircuit closed position, means for flexibly mounting said xed arcingcontact for self-alignment during contact engagement with said movablearcing contact, said switch blade actuating means separating said arcingcontacts immediately following disengagement of said switch blade fromsaid stationary contact during circuit opening operation, insulatingshield means arranged between said stationary contact and said hornshaped fixed arcing contact to protect said stationary contact from arcnames and hot gases formed at the point of break of said arcingcontacts, said arc runners transferring said arc from the region of arcinitiation to a region of said chute containing said barrier plates,said arc runners being arranged to elongate said arc to the width ofsaid arc 10 chute before introducing said arc into said barrier plates.

5. in electric circuit interrupting device corriprising a stationarycontact, a movable switch blade, means for moving said switch blade intoand out or' engagement with said stationary contact, an arcextinguishing device kcomprising an arc chute, a plurality of barrierplates arranged within said arc chute, and a pair of spaced hat metallicarc runners, cooperating fixed and movable arcing contacts between whichali arc is ignited when the circuit is interrupted mounted adjacent saidarc extinguishing device, said arcing contacts comprising a slotted hornshaped fixed arcing contact electrically connected to said stationarycontact and a movable arcing Contact comprising a portion of said switchblade firmly engaging the slot walls of said fixed arcing contact whenin circuit closed position, means for flexibly mounting said fixedarcing contact for self-alignment during contact engagement with saidmovable arcing contact, said switch blade actuating means separatingsaid arcing contacts immediately following disengagement oi' said switchblade irom said stationary Contact during circuit opening operation,insulating shield means arranged between said stationary contact andsaid horn shaped fixed arcing contact to protect said stationary contactfrom arc names and hot gases formed at the point of breaK or said arcingcontacts, said arc runners comprising diverging sections arrangedadjacent the fully open positions of the dinerent said arcing contactsfor receiving said arc trom said arcing contacts and elongating said arcto the Width of said chute and sections extending substantially parallelto the longitudinal axis of said chute, said diverging sections` of saidarc runners being arranged to elongate said arc in a directionperpendicular to said barrier plates to the full width of said arc chutebefore introducing said arc into said barrier plates.

6. An electric circuit interrupting device coniprising a stationarycontact, a movable switch blade, means for moving said switch blade intoand out of engagement with said stationary contact, an arc extinguishingdevice comprising an arc chute, a plurality of barrier plates arrangedwithin said arc chute, and a pair of spaced flat metallic arc runners,cooperating fixed and movable arcing contacts between which an arc isignited when the circuit is interrupted mounted adjacent said arcextinguishing device, said arcing contacts comprising a slotted hornshaped fixed arcing contact electrically connected to said stationarycontact and a movable arcing contact comprising a portion of said switchblade firmly engaging the slot walls of said fixed arcing contact whenin circuit closed position, means for flexibly mounting said xed arcingcontact for self-alignment during contact engagement with said movablearcing contact, said switch blade actuating means separating said arcingcontacts immediately following disengagement of said switch blade fromsaid stationary contact during circuit opening operation, insulatingshield means arranged between said stationary contact and said hornshaped fixed arcing contact to protect said stationary contact from arcflames and hot gases formed at the point of break of said arcingcontacts, said arc runners comprising diverging sections extendingadjacent the fully open positions of the difereiit said arcing contactsfor receiving said arc from said arcing contacts, and blowout means fortransferring said aro from said arcing contacts References Cited in thefile of this patent to said dii/erging sections, said arc rnnners coop-UNITED STATES PATENTS erating with said blowout means to initiallyrapidly elongate said arc in a direction perpendicu- Number Name Datelar to the longitudinal axis of said chute and to 5 1301573 Wllms M31314' 1933 introduce the terminal end sections of said arc 2,227,507 Macfelu Jan- 7: 1941 into said barrier plates after the introduction of21242905 Dckmon et al- ---v May 20 1941 the center section of said arcinto said barrier 2,259,971 Cummlng et al Oct 21 1941 plates but beforethe center Asection of said arc 276,359 Nall Man 14, 1942 has materiallyheated said barrier plates. 10 FOREIGN PATENTS C. KET-LE. Number CountryDate 561,512 Great Britain May 23, 1944

